diff --git a/av/frame.pxd b/av/frame.pxd
index e0d5b42..57fbc47 100644
--- a/av/frame.pxd
+++ b/av/frame.pxd
@@ -19,3 +19,5 @@ cdef class Frame(object):
     cdef _copy_internal_attributes(self, Frame source, bint data_layout=?)
 
     cdef _init_user_attributes(self)
+
+    cdef _add_cc_data(self, buffer, lib.AVFrameSideDataType type)
diff --git a/av/frame.pyx b/av/frame.pyx
index 3717ddc..94b3d8b 100644
--- a/av/frame.pyx
+++ b/av/frame.pyx
@@ -2,7 +2,7 @@ from av.utils cimport avrational_to_fraction, to_avrational
 
 from fractions import Fraction
 
-from av.sidedata.sidedata import SideDataContainer
+from av.sidedata.sidedata import SideDataContainer, SideData
 
 
 cdef class Frame(object):
@@ -66,6 +66,13 @@ cdef class Frame(object):
 
         self._time_base = dst
 
+    def add(self, buffer, type):
+        self._add_cc_data(buffer, type)
+    
+    cdef _add_cc_data(self, buffer, lib.AVFrameSideDataType type):
+        data = SideData(self, buffer, type)
+        # Need to update self._side_data
+
     property dts:
         """
         The decoding timestamp in :attr:`time_base` units for this frame.
diff --git a/av/sidedata/sidedata.pxd b/av/sidedata/sidedata.pxd
index f30d8fe..d736850 100644
--- a/av/sidedata/sidedata.pxd
+++ b/av/sidedata/sidedata.pxd
@@ -11,6 +11,7 @@ cdef class SideData(Buffer):
     cdef Frame frame
     cdef lib.AVFrameSideData *ptr
     cdef _Dictionary metadata
+    cdef int writable
 
 
 cdef SideData wrap_side_data(Frame frame, int index)
diff --git a/av/sidedata/sidedata.pyx b/av/sidedata/sidedata.pyx
index ec7de59..befd548 100644
--- a/av/sidedata/sidedata.pyx
+++ b/av/sidedata/sidedata.pyx
@@ -4,6 +4,9 @@ from collections.abc import Mapping
 
 from av.sidedata.motionvectors import MotionVectors
 
+from libc.string cimport memcpy
+
+from av.bytesource cimport ByteSource, bytesource
 
 cdef object _cinit_bypass_sentinel = object()
 
@@ -52,6 +55,15 @@ cdef class SideData(Buffer):
         self.frame = frame
         self.ptr = frame.ptr.side_data[index]
         self.metadata = wrap_dictionary(self.ptr.metadata)
+        self.writable = False
+
+    def __init__(self, Frame frame, bytes, lib.AVFrameSideDataType type):
+        cdef ByteSource source = bytesource(bytes)
+        self.frame = frame
+        self.ptr = lib.av_frame_new_side_data(frame.ptr, type, source.length)
+        self.metadata = wrap_dictionary(self.ptr.metadata)
+        self.writable = True
+        memcpy(self.ptr.data, source.ptr, source.length)
 
     cdef size_t _buffer_size(self):
         return self.ptr.size
@@ -60,7 +72,7 @@ cdef class SideData(Buffer):
         return self.ptr.data
 
     cdef bint _buffer_writable(self):
-        return False
+        return self.writable
 
     def __repr__(self):
         return f'<av.sidedata.{self.__class__.__name__} {self.ptr.size} bytes of {self.type} at 0x{<unsigned int>self.ptr.data:0x}>'
@@ -99,6 +111,8 @@ cdef class _SideDataContainer(object):
         type_ = Type.get(key)
         return self._by_type[type_]
 
+    def add(self, buffer, type):
+        self.frame.add(buffer, type)
 
 class SideDataContainer(_SideDataContainer, Mapping):
     pass
diff --git a/examples/numpy/generate_video.py b/examples/numpy/generate_video.py
index 80145d5..939d414 100644
--- a/examples/numpy/generate_video.py
+++ b/examples/numpy/generate_video.py
@@ -1,15 +1,41 @@
 import numpy as np
 
 import av
+from av.sidedata.sidedata import Type
 
+class CC608Data():
+    cc_type_byte = 0xfc # Field 1
+    odd_parity = bytearray([0] * 128)
+    idx = 0
+    for idx in range(128):
+        if idx.bit_count() & 1:
+            odd_parity[idx] = idx
+        else:
+            odd_parity[idx] = idx | 0x80
 
-duration = 4
+    def __init__(self):
+        self.ba = bytearray()
+
+    def appendPair(self, cc_data_1, cc_data_2):
+        self.ba.append(self.cc_type_byte)
+        self.ba.append(self.odd_parity[cc_data_1])
+        self.ba.append(self.odd_parity[cc_data_2])
+
+    def appendString(self, string):
+        bytes = bytearray(string.encode('ascii'))
+        if len(bytes) & 1:
+            bytes.append(0)
+        for i in range(0, len(bytes), 2):
+            self.appendPair(bytes[i], bytes[i+1])
+
+
+duration = 20
 fps = 24
 total_frames = duration * fps
 
 container = av.open("test.mp4", mode="w")
 
-stream = container.add_stream("mpeg4", rate=fps)
+stream = container.add_stream("libx264", rate=fps)
 stream.width = 480
 stream.height = 320
 stream.pix_fmt = "yuv420p"
@@ -24,6 +50,18 @@ for frame_i in range(total_frames):
     img = np.round(255 * img).astype(np.uint8)
 
     frame = av.VideoFrame.from_ndarray(img, format="rgb24")
+
+    if (frame_i % fps) == 0:
+        # Add pop-on closed caption
+        data = CC608Data()
+        data.appendPair(0x14, 0x20) # RCL
+        data.appendPair(0x14, 0x2e) # ENM
+        data.appendPair(0x14, 0x60) # Row 15, White
+        data.appendString("CC1: 00:%02d:%02d" % ((frame_i/(60*fps))%60, (frame_i/fps)%60))
+        data.appendPair(0x14, 0x2c) # EDM
+        data.appendPair(0x14, 0x2f) # EOC
+        frame.side_data.add(data.ba, Type.A53_CC)
+
     for packet in stream.encode(frame):
         container.mux(packet)
 
diff --git a/include/libavutil/frame.pxd b/include/libavutil/frame.pxd
index aa8dc3a..7dd1d8e 100644
--- a/include/libavutil/frame.pxd
+++ b/include/libavutil/frame.pxd
@@ -12,3 +12,4 @@ cdef extern from "libavutil/frame.h" nogil:
     cdef int av_frame_copy(AVFrame *dst, const AVFrame *src)
     cdef int av_frame_copy_props(AVFrame *dst, const AVFrame *src)
     cdef AVFrameSideData* av_frame_get_side_data(AVFrame *frame, AVFrameSideDataType type)
+    cdef AVFrameSideData* av_frame_new_side_data(AVFrame *frame, AVFrameSideDataType type, int size)